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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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CHAPTER X
THE EARTHQUAKE ADVANCE THEORY
The Problem. The facts stated in the previous chapters make it clear that the glaciers of Yakutat Bay have in recent years been undergoing a series of changes of unusual character. From a state of stagnation a number of them have sprung into sudden activity and then, with almost equal abruptness, have relapsed again into a state of stagnation. The transformation has affected different glaciers at different times and in different degree, and some of the glaciers have not been affected at all. So far as we know, such spectacular changes have not hitherto been recorded. The advance of Vernagt-Ferner in the Tyrolese Alps is a case analogous to these, but is only a single instance in a glaciated region, and it differs in notable respects from the advancing Yakutat Bay glaciers. The advance of two glaciers in Icy Fiord, Spitsbergen, and the advance of glaciers reported from the Himalayas are too little known to offer basis for comparison. The solution of the problem of the cause for these changes must, therefore, be based mainly upon the facts which the Yakutat Bay region presents.
Upon the basis of the comparative observations of 1905 and 1906 the senior author has proposed the theory of avalanching during earthquake shaking, rather than increase of snowfall with climatic oscillations, as the explanation of the phenomena of advancing glaciers in this region.1 The observations of 1909, 1910, and 1913 add important and significant facts to those previously observed, and among these facts are several tending toward the verification of the theory, and none opposed to it. With these new facts we are in a position to more fully discuss this theory than was hitherto possible. This discussion will be prefaced by a summary of the significant facts of observation which have already been presented in some detail under the description of the individual glaciers.
Summary of the Phenomena. In recent years, up to Gilbert's visit in 1899, the general history of the Yakutat Bay glaciers had been one of recession; and in most of them the recession continued to 1905, and in some even to 1918. This recession was apparently a stage in the withdrawal of the glaciers from positions to which they had readvanced after a period of recession even greater than the present. During this earlier advance Nunatak Glacier had pushed northwestward into the lower portion of Russell Fiord, and also southward up the fiord until it joined the Hidden Glacier and the united ice stream advanced far up toward the head of the fiord. From this advanced position the recession of the glaciers has been both rapid and recent, and in the case of the Hidden Glacier has continued until 1906 or 1907, and in the Nunatak Glacier until 1909. It is not certain that this recession was not interrupted by halts or minor advances; but there is no evidence of this, and certainly, during the period of observation, that is
* Tarr, R. S., Recent Advance of Glaciers in the Yakutat Bay Region, Alaska, Bull. Geol. Soc. Amer., Vol. 18, 1007, pp. 277-286; The Yakutat Bay Region, Alaska, Professional Paper 04, U. S. Geol. Survey, 1909, pp. 90-95; The Theory of Advance of Glaciers in Response to Earthquake ShuTting, Zeitschrift ftlr Gletscherkunde, Band V, 1910, pp. 1-85; Tarr, R. S. and Martin, Lawrence, Professional Paper 69, TJ. S. Geol. Survey, 1912, pp. 51-61.
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